This invention relates generally to solvent extraction and more particularly to a fat extraction process and apparatus which are well suited for automated operation.
Solvent extraction of fats and other substances has conventionally been carried out by a process known as the Soxhlet process. In the Soxhlet process, solvent is heated in a flask to vaporization, and the rising vapors are condensed on a cooling coil. The condensate drips onto a sample which is held below the cooling coil in a thimble. When the solvent level in the thimble rises above the sample, the solvent is siphoned off through a siphon tube and returned to the flask. The process is repeated continuously.
The main disadvantage of the Soxhlet process is the relatively long time that is required to complete the extraction. In addition, insertion and removal of the sample requires removal of the cooling coil along with its inlet and outlet connections. Another problem is that residual solvent recovery in the extraction unit is not possible.
A higher speed extraction process has been developed which involves boiling of the solvent while the sample is immersed in it. The solvent vapors are condensed on a cooling coil and drip back into the sample vessel. When the boiling phase of the process has been completed, the sample is lifted out of the solvent through manual operation of a cable system attached to the thimble that holds the sample. With the sample held above the level of the solvent, a washing phase of the process is carried out. During the washing phase, the solvent condensate drips onto the sample and back into the sample vessel. A solvent recovery phase is carried out by closing a manual shut-off valve which causes the solvent condensate to be collected in a collection chamber in the extraction unit. Following removal of the sample, the shut-off valve can be opened to drain the solvent from the collection chamber into a beaker.
Although this process is faster than the Soxhlet process, it is not altogether satisfactory, primarily because of the physical movements and the large number of manual operations that are required. During each cycle, the sample must be raised, the shut-off valve must be opened and closed, and the recovered solvent must be manually collected. Effective automation of fat extraction processes has proven to be technically difficult and unduly expensive, especially for continuous extraction units of the type used in laboratories.
The present invention has, as its principal goal, the provision of an improved fat extraction process which is carried out at automatically high speed. In accordance with the invention, four phases or steps are carried out in succession. First, the sample is boiled in solvent with simultaneous condensation and return of the condensate. Then, the solvent level is reduced until it is below the sample. Next, the sample is washed and wetted while remaining out of the solvent. Finally, the solvent is recovered in a collection vessel.
It is a particularly important feature of the invention that each phase of the extraction process is automatically initiated and terminated by a simple timer. The timer controls a valve which in turn causes an open topped funnel either to overflow or to drain the solvent condensate into an external collection vessel. Thus, all phases of the process are controlled automatically by the timer, and human intervention is required only during insertion and removal of the sample.
The invention is further directed to extraction apparatus on which the process can be carried out without mechanical movements or complicated parts. Because the drain valve determines whether or not the condensate will overflow from the funnel, the solvent level is wholly controlled by the valve and there is no need to raise or lower the sample or carry out other mechanical movements in the extraction unit.
By virtue of its nature, the apparatus of the present invention is well suited to process numerous samples simultaneously in different extraction units. The drain tubes of the different units should converge upstream from the control valve, thus draining the recovered solvent from each unit into a single collection vessel with only a single valve required for the plural extraction units. In this way, increased capacity can be provided for the processing of samples and a central collection system is provided for collecting all of the solvent that is recovered.